The invention relates to the field of composite materials and more particularly to composite materials comprising, on at least one of their surfaces, an impact-resistant primer layer and at least one abrasion-resistant (scratch-resistant) coating layer deposited on the primer layer. The impact-resistant primer layer is formed from polymer particles dispersed in water. The scratch-resistant coating may consist, for example, of a photocrosslinkable or thermally crosslinkable varnish according to EP 0,035,609 or WO 83/0125. The composite materials intended by the present invention are intended for various applications. By way of non-limiting indication, applications in the building industry, such as windows, in the automobile industry, such as windows and headlight lenses, and in the sanitaryware industry, such as shower trays and bathtubs, may be mentioned.
Known composite materials have their impact-resistance properties altered by the presence of a hard surface layer. Moreover, in certain applications good solvent resistance is demanded.
It is well known that those composite materials intended for the applications described above with no primer layer have a low impact resistance and a limited resistance to the action of solvents when these composite materials are under stress (xe2x80x9cstress crackingxe2x80x9d).
The prior art discloses impact-resistant layers of various kinds. Thus, Japanese patents 6,314,001 and 6,387,223 describe an impact-resistant primer layer based on a thermoplastic polyurethane resin.
U.S. Pat. No. 5,015,523 recommends the use of acrylic impact-resistant primers, however European Patent EP-0,404,111 describes the use of impact-resistant primers based on a thermosetting polyurethane.
Document U.S. Pat. No. 5,316,791 describes the use of an impact-resistant primer layer formed from an aqueous polyurethane dispersion applied directly to one surface of an organic glass substrate. The impact-resistant primer layer may be obtained by drying and curing, in air, an aqueous dispersion or latex of a polyurethane which may possibly contain an anionically stabilized acrylic emulsion.
Although these impact-resistant primer layers of the prior art ensure both acceptable adhesion of the abrasion-resistant hard coating and a degree of impact resistance, the latter is not sufficient for the applications intended.
It has now been found that it is possible to improve the impact-resistance of composite materials by using, for the impact-resistant primer layer, an aggregate of multiphase structured particles, one of the phases of which is formed by a polymer having a soft character and another phase is formed by a polymer having a hard character, these phases having glass transistion temperatures lying within defined ranges.
According to the invention, a multilayer composite material is produced which comprises a substrate, at least one impact-resistant primer layer deposited on at least one of the faces of the substrate, and at least one abrasion-resistant coating layer deposited on the primer layer, characterized in that the said primer layer comprises an aggregate of multiphase polymer particles, each particle comprising two separate phases:
a first phase formed by a polymer P1 with a soft character having a glass transition temperature (Tg1) below 20xc2x0 C., and
a second phase formed by a polymer P2 with a hard character having a glass transition temperature (Tg2) above 50xc2x0 C.
Preferably, the particles are two-phase particles and possess a core/shell structure.
Preferably, the core contains the polymer P1 and the shell contains the polymer P2.
Also preferably, the polymer P1 has a Tg1 below 0xc2x0 C. and the polymer P2 has a Tg2 above 60xc2x0 C.
Again preferably, the polymer P1 is dispersed in the form of nodules in a matrix formed by the polymer P2.
Preferably, the polymer P1 has a hydrophobicity greater than that of the polymer P2.
In general, the impact-resistant primer layer consists of 70 to 90% by weight of the polymer P1 with a soft character and 10 to 30% by weight of the polymer P2 with a hard character.
Advantageously, the polymers P1 and P2 of the primer layers according to the invention contain:
90 to 100% by weight of units obtained by the polymerization of at least one monomer chosen from the group (I) consisting of (C1-C8)alkyl esters of (meth)acrylic acid, such as methyl (meth)acrylate and butyl (meth)acrylate; vinyl esters of linear or branched carboxylic acids, such as vinyl acetate and vinyl stearate; styrene; alkylstyrenes, such as xcex1-methylstyrene; haloalkylstyrenes, such as chloromethylstyrene; conjugated dienes, such as butadiene and isoprene; (meth)acrylamide; acrylonitrile; vinyl chloride; (meth)acrylic acids and their derivatives, such as anhydrides; and
0 to 10% by weight of units obtained by the polymerization of at least one monomer chosen from the group (II) consisting of allyl esters of xcex1, xcex2-unsaturated monocarboxylic or dicarboxylic acids, such as allyl acrylate, allyl methacrylate and diallyl maleate; conjugated dienes, such a butadiene and isoprene; polyol poly(meth)acrylates, such as ethylene glycol dimethacrylate, 1,3-butylene glycol diamethacrylate, 1,4-butenediol diacrylate and pentaerythritol tetraacrylate; polyvinylbenzenes, such as divinylbenzene or trivinylbenzene; and polyallyl derivatives, such as triallyl cyanurate and triallyl trimesate.
The monomers of group (II) act as crosslinking agents in the polymers P1 and P2.
In general, the polymer P1 with a soft character consists mostly of units coming from the polymerization of at least one monomer chosen from butyl acrylate, butadiene and isoprene, however the polymer P2 with a hard character in general consists mostly of units coming from the polymerization of at least one monomer chosen from methyl methacrylate, styrene and vinyl chloride.
In the case of a core/shell structure, preferably only the core is crosslinked, the preferred crosslinking monomers being butadiene and 1,4-butanediol diacrylate and the content of crosslinking monomers being between 0 and 10% by weight with respect of the total weight of the particles.
The hard polymer P2 may be grafted directly onto the polymer P1 or by introducing into the latter residues of monomer units. These residues of monomer units are obtained by the incorporation, into the soft polymer P1, of grafting monomers chosen either from conjugated dienes, the residues of monomer units resulting from the partial 1,2-incorporation of the diene during polymerization, or from allyl esters of xcex1, xcex2-unsaturated carboxylic or dicarboxylic acids, which possess two copolymerizable functional groups of different reactivities.
The preferred grafting monomers according to the invention are butadiene, allyl methacrylate and diallyl maleate.
The polymers P1 and P2 according to the invention may be prepared by two-step emulsion polymerization, as described below, using monomers chosen from group (I) and possibly group (II) above.
The selection of the monomers both for the soft polymer P1 and for the hard polymer P2 depends on properties, such as the hydrophobicity and the glass transition temperature, that it is desired to confer on the polymers in question.
The primer layer according to the invention may be obtained in particular from a latex containing particles of the polymers P1 and P2, particularly hydrophobic and core/shell-structured polymers P1 and P2. When the mass contribution of the shell in total weight of the polymer particles does not exceed 30%, the latex applied to one surface of an organic glass substrate gives, after low-temperature drying, and without the intervention of either coalescing agents or of volatile organic compounds, a continuous film, structured in the form of soft nodules dispersed in a homogeneous, hard matrix, having no surface tack and having good mechanical strength.
In general, hydrophobicity is the property of being insoluble in water or the absence of affinity for water. According to the invention, this lack of affinity may be hierarchized. In fact, the hydrophobicity according to the invention is defined by the solubility parameter ( ) as described in xe2x80x9cProperties of polymersxe2x80x9d by D. W. Van Krevelen, 1990, 3rd edition, page 200. This parameter makes it possible to classify the various polymers according to their affinities for water. According to the invention, a polymer is hydrophobic if its ( ) is less than 26. In addition, if (1) of a polymer 1 is less than (2) of a polymer 2, then polymer 1 is more hydrophobic than polymer 2.
A latex suitable for producing the primer layers according to the invention is a latex which contains neither coalescing agents nor volatile organic compounds and is film-forming by evaporation at a temperature below 40xc2x0 C. and preferably close to 250xc2x0 C., the latex being based on core/shell-structured particles of hydrophobic polymers, the particles consisting of:
70 to 90% by weight of at least one polymer P1 with a soft character, having a Tg below 20xc2x0 C., forming the core, and of
10 to 30% by weight of at least one polymer P2 with a hard character, having a Tg above 50xc2x0 C., forming the shell.
Preferably, the core has a Tg1 below 0xc2x0 C. and the shell has a Tg2 above 60xc2x0 C. In addition, the core is generally more hydrophobic than the shell.
The latices of the invention are prepared in two steps, by emulsion polymerization of a monomer mixture consisting of:
from 90 to 100% by weight of at least one monomer chosen from group (I) and
from 0 to 10% by weight of at least one monomer chosen from group (II).
In general, the latices are prepared by emulsion polymerization in at least two steps, using the polymerization techniques well known to those skilled in the art.
The composition of the mixture of monomers to be polymerized at each step depends on the character that it is desired to give to the polymers formed in that step (Tg, hydrophobicity).
According to the invention, the polymer P1 with a soft character and having a Tg1 below 20xc2x0 C., constituting the core of the particles, is prepared in a first step and then the preparation of the polymer P2 having a Tg2 above 50xc2x0 C., constituting the shell with a hard character, is carried out.
It will be noted that, in order for the particles to be perfectly structured, the mixture of monomers to be polymerized in order to form the core must be more hydrophobic than that to be polymerized in order to form the shell.
For each step, the polymerization reaction is preferably carried out in an inert atmosphere in the presence of radical initiators. The initiation system used may be an oxidation-reduction system, a thermal or peroxide system such as sodium bisulphate or di-isopropylbenzene/tert-butyl hydroperoxide, the amounts used being between 0.2 and 1% by weight with respect to the total weight of the monomers, preferably between 0.25 and 0.5% by weight.
The emulsion polymerization reaction according to the invention is carried out at a temperature between 25 and 150xc2x0 C., the temperature epending on the nature of the initiation system used.
The preparation of the dispersions according o the invention is preferably carried out using a emicontinuous-type process making it possible to limit the derivatives of the compositions which depend on the differences in reactivity of the various monomers. The introduction of the monomers, which are either pure or in the form of a pre-emulsion with some of the water and surfactants, is thus generally carried out over a period of time ranging from 3 hours 30 minutes to 5 hours. It is also useful, although not absolutely necessary, for there to be seeding of 1 to 15% of the monomers. The emulsifying systems used in the emulsion polymerization process are chosen from the range of emulsifiers possessing a suitable hydrophilic/lipophilic balance. The preferred systems consist of the combination of an anionic surfactant, such as sodium lauryl sulphate, nonylphenol ethoxylate sulphates, particularly those with 20-25 mol of ethylene oxide, dodecyl benzene sulphonate and fatty-alcohol ethoxylate sulphates, and of a non-ionic surfactant, such as nonylphenyl ethoxylates, particularly those with 10-40 mol of ethylene oxide, and fatty alcohol ethoxylates.
Advantageously, the substrates or supports are chosen from among:
transparent or non-transparent organic materials;
mineral glasses.
Among transparent organic materials figure especially:
poly(methyl methacrylate) and its copolymers;
impact-modified poly(methyl methacrylate) and its copolymers;
polycarbonates;
styrene/acrylonitrile copolymers;
polystyrene and its copolymers;
polyesters of the PET or PETG type;
cycloolefin copolymers;
poly(vinylchloride) and its copolymers.
Among non-transparent organic materials figure especially:
poly(vinylidene fluoride) and its copolymers;
impact polystyrenes;
ABS copolymers;
or their alloys based on one of the above polymers.
Advantageously, the substrate is made of impact-modified poly(methyl methacrylate) or of its impact-modified copolymers, for example a poly(methyl methacrylate) or one of its copolymers containing at least 10% by weight of an impact modifier of the hard/soft/hard type prepared according to U.S. Pat. No. 2,159,882 or of the soft/hard type prepared according to U.S. Pat. No. 2,092,389.
Advantageously, the substrate is made of polycarbonate.
The mineral or organic glasses are generally those used for lenses and/or windows. Among them may be mentioned the substrates obtained by the polymerization of alkyl methacrylates, particularly C1-C4 alkyl methacrylates, such as methyl (meth)acrylate and ethyl (meth)acrylate; allyl derivatives, such as allyl carbonates of linear or branched, aliphatic or aromatic polyols; thio(meth)acrylics; thiourethanes, and polyethoxylated aromatic (meth)acrylates, such as polyethoxylated dimethacrylate bisphenolates.
Among the recommended substrates, mention may be made of substrates obtained by the polymerization of allyl carbonates of polyols among which mention may be made of ethylene glycol bis(allyl carbonate), diethylene glycol bis(2-methyl carbonate), diethylene glycol bis(allyl carbonate), ethylene glycol bis(2-chloro allyl carbonate), triethylene glycol bis(allyl carbonate), 1,3-propanediol bis(allyl carbonate), propylene glycol bis(2-ethyl allyl carbonate), 1,3-butenediol bis(allyl carbonate), 1,4-butenediol bis(2-bromoallyl carbonate), dipropylene glycol bis(allyl carbonate), trimethylene glycol bis(2-ethylallyl carbonate), pentamethylene glycol bis(allyl carbonate) and isopropylene bisphenol-A bis(allyl carbonate).
The acrylic polymers may also be copolymers formed from methyl methacrylate and from comonomers such as (meth)acrylic acid, alkyl (meth)acrylates, hydroxyalkyl (meth)acrylates, alkoxyalkyl (meth)acrylates in which the alkyl group is, for example, from 1 to 8 carbon atoms, (meth)acrylonitrile, (meth)acrylamide, maleimide, maleic anhydride, substituted or unsubstituted styrene, and a diene such as butadiene. As substrate that can be treated according to the invention, mention may also be made of the above (co)polymers in imidized form, for example polymers having glutarimide groups; the imidized copolymers may also contain methyl methacrylate, methacrylic acid, glutaric anhydride and, possibly, methacrylamide groups, it being possible for the amide or imide groups to carry identical or different substituents in the same chain.
The present invention also relates to:
building and motor-vehicle windows,
motor-vehicle headlights,
sanitaryware, especially shower trays, wash basins and bathtubs,
these comprising the composite materials according to the present invention as described above.